This invention relates generally to an optical lens with patterned nano-structures that collimates light from a light-emitting surface in close proximity.
The use of light is ubiquitous and can be found in applications ranging from image capture, microscopy and telecommunications, as just three examples. Efficiently directing light towards the object(s) of interest typically requires collimating the light, which has for centuries been achieved using lenses. The further the distance to the object to the illuminated, the longer the distance the light has to propagate and the more collimated it has to be. Lenses are traditionally curved glass surfaces which collect light distributed over a range of angles and redirect it to have different angles. This is explained by the principle of refraction in which light travels at different speeds in materials of different index of refraction. As light crosses through a material interface at an oblique incident angle, it will bend towards or away from the angle that is normal to the interface surface, if the latter material has a larger or smaller index of refraction, respectively. The physics are well described by a ‘ray-optics’ treatment commonly taught in high school, in which only a few parameters such as the wavelength, the lens material's index of refraction, and the overall geometry are considered (ref. Snell's Law). The ray-optics treatment, and hence design and application, relies on the assumption that the curvature of the lens is large compared to the wavelength and beam size. Typically, light from a source is collimated by placing the source at the focal distance from the lens. Light emitted from most sources such as bulbs, Light Emitting Diodes (LEDs), and Organic LEDs spreads as it propagates and thus lenses designed for these sources typically need to be much larger than the light source, in order to maximize light collection efficiency. The restrictions imposed by these bulky lenses have therefore conventionally limited their use to “far-field” imaging, where only light emitted from the light source at small incident angles to the lens is able to propagate an appreciable distance. Light that is going straight, i.e. having a zero angle relative to the optical axis, can propagate further than light at higher angles. High-angle light that enters the lens either undergoes internal reflection and does not propagate at all, or else it is not sufficiently collimated, so that it is still at a high angle as it exits the lens, and propagates only a short distance.